In principle, a typical induction motor includes at a minimum a central rotor surrounded by a stator. The stator includes windings through which an electrical current flows to produce a magnetic field. The magnetic field interacts with the rotor thereby causing the rotor to rotate.
Induction motors are relatively efficient in converting electrical energy into mechanical energy and as a result there is an increasing interest in such motors in a variety of applications, including in the automotive field. Induction motors may, for example, find increasing application in hybrid powered vehicles that use a combination of an internal combustion engine and one or more electric motors to provide motive power. Electrical induction motors find application in other areas as well as providing supplemental motive power. For example, induction motors may provide power to a range of accessories that might otherwise be powered via hydraulic or other systems that are driven by an internal combustion engine. With increasing applications in the automotive field, there is also a need for induction motors that conform to desired design parameters such as vehicle total mass, vehicle mass distribution, vehicle packaging that imposes space limitations, and cost and ease of mass production.
Induction motor rotors can be costly to build because they are currently often made by die casting and then machining the die cast rotor. FIGS. 1-2 illustrate an example of three stages of making a typical rotor 10. The final rotor 10 shown in FIG. 1 includes a stacked series of consolidated steel laminations 40, seen more clearly in FIG. 2 in pre-consolidated form. FIG. 2 illustrates circular steel laminations 20 arrayed in a vertical stack 30. These laminations each have a central circular hole 24 and each lamination has a perimeter that includes a series of slots 22. Typically, these laminations 20 are stacked and are then consolidated by die casting, while also forming a lower end ring 32 and an upper end ring 38, as shown in FIG. 1. In the die casting process, molten aluminum flows between the slots 22 of the stacked laminations to consolidate the laminations 20 and also to form the upper end ring 38 and lower end ring 32, shown in FIG. 1, after appropriate post-casting machining.
The above-described process imposes limitations on manufacturing rotors. For example, metals and materials are restricted to those suitable for use in die casting processes. There may have to be a trade-off between materials desired and the castability of the materials. For example, aluminum alloy 6101-T6 might be a desirable fabrication material for rotors due to its strength and electrical properties. However, this alloy's affinity for iron causes accelerated die wear and thereby increases rotor cost. Thus, die casting process-related properties of a material may discourage its use even if it is potentially better and/or less expensive. Die casting process-related properties may also preclude the use of materials that might be expected to improve the performance of the induction motor because the materials cannot be die cast. Further, die casting may require additional step of post-casting machining of the rotor, which imposes additional costs.
Accordingly, it is desirable to develop processes for manufacturing induction motor rotors that do not have the limitations of the die casting method with respect to materials selection. In addition, it is desirable that the processes minimize post-production rotor machining requirements, if any, to reduce costs. Further it is desirable that the processes produce rotors that have superior characteristics in at least some respects, for example in terms of lighter weight, lower cost, decreased porosity, more electrical effectiveness and/or allow improved designs, for example, through better packaging based on more compact rotors and induction motors. Furthermore, other desirable features and characteristics of the processes and rotors will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.